Unknitting is simply where you go back to where your error is by stitch by stitch putting your left needle in the stitch you just knit into and then slowly pulling it off the right needle and tightening the tension to erase the stitch. Be sure to have the left needle there to pick it up, though, or you will have a dropped stitch. It's a slower but safer way to frog back to where you want to fix. The other option is to take the needle out and rip back which is really only a good idea if your mistake is quite a few rows back since it is easier to drop stitches that way.
Hope that helps!
Just one more row...
OTN: Chunky Knit Scarf; Baby Sweater; Mitts